The progress of microelectronic devices toward higher integration has created an increasing demand for the photolithography capable of forming a pattern with reduced feature size. At an initial stage of photolithography, a coating is often deposited on a synthetic quartz glass substrate. As the feature size of wiring pattern is reduced, the deposition technique which is free of coating variations is desired. For this and other reasons, it becomes requisite that the synthetic quartz glass substrate is stored so as to avoid any detrimental effect of chemicals which would otherwise adsorb to the substrate, prior to the coating deposition.
The effect of adsorbed chemicals is detrimental particularly on synthetic quartz glass substrates for liquid crystal-related photomasks. Since the liquid crystal photomask-forming synthetic quartz glass substrates are generally of large size, a container tends to receive a limited number of substrates on account of awkward manipulation. In the case of rectangular substrates having a long side in excess of 500 mm, for example, the container receives a single substrate. As the number of substrates accommodated in a container is limited, the inside surface area of the container becomes larger compared with the surface area of the substrates, indicating a probability that the substrates are more susceptible to contamination by outgassing from the container material.
Since photomask-forming synthetic quartz glass substrates of large size are manufactured through an extended process, their production architecture is often designed with an adequate margin. Specifically, glass substrates ready for use are accommodated in individual containers and stored as stocks for a long period of time. This tendency also worsens the problem of contamination by outgassing from the container material.
For preventing the influence of adsorbing chemicals, JP-A 2004-153221, JP-A 2004-179449, and JP-A 2004-193272 describe a container provided with a filter containing activated carbon and ameliorate the mechanism of the filter. Since the pressure difference between the interior and the exterior of the container is minimized or eliminated, these containers allegedly prevent contamination from the ambient atmosphere due to a pressure difference occurring during transportation. They provide an unsatisfactory countermeasure to outgassing within the container due to the container material.
JP-A 8-148551 describes a substrate container provided with a blower and activated carbon for removing organic matter. JP-A 2000-174109 describes a container having disposed therein a fan, a chemical filter, and a desiccant such as activated carbon wherein the fan is operated to circulate the air within the container to maintain a cleanness. The containers of these two patents may perform well when the substrates are stored at a certain place. However, they are unsuited in an application where the substrates are transported to a certain destination because the container is provided with a fan or circulation mechanism of electric drive. That is, these containers are unsuited for shipment to end users.